Initial studies on horizontal transmission of channel catfish virus (CCV) in selected catfish fingerling ponds in Mississippi

Little is known about the dynamics of natural transmission of channel catfish virus (CCV). Horizontal transmission was evaluated in pond environments by (1) stocking CCV-infected fish with non-infected fish and (2) by exposing fish to water from a pond with CCV-infected fish. This study produced no overt disease, but transmission was apparent in the cohabitation systems suggesting that fish-to-fish contact is important for horizontal transmission. A study to determine interaction of CCV with pond water showed that nearly all virions were bound to suspended particulates, which were removed by filtration before cell culture. However, if these suspensions were injected into channel catfish, culturable virus could be detected from the posterior kidney within 48 hours, allowing the use of limiting dilutions to quantitate CCV. Samples of channel catfish fry from five farms were assayed using polymerase chain reaction and all populations sampled demonstrated a high presence of latent CCV infection.